The present invention relates to a flow control valve, especially for use in refrigeration systems for controlling the flow of refrigerant.
A refrigeration system typically includes a compressor, a condenser, an evaporator, and a flow control valve which meters the flow of refrigerant to the evaporator and converts liquid refrigerant to a mixture of liquid and vapor. The flow control valve is positioned upstream of the evaporator where it functions as an expansion valve for converting high pressure, sub-cooled liquid refrigerant into a low pressure, low-temperature mixture of liquid and vapor. Also, a flow control valve could be positioned downstream of the evaporator (i.e., between the evaporator and the compressor) where it functions as a suction valve for regulating evaporation pressure in the evaporator.
The flow control valve typically comprises fluid inlet and outlet passages interconnected by a connecting port that is bordered by a valve seat. A valve element is arranged be moved toward and away from the valve seat by an actuator, such as an electric solenoid or stepping motor.
When such a flow control value is being used as a suction valve in a refrigeration system, the size of the connecting port must be large enough to accommodate an ample flow therethrough during conditions of low pressure drops. Due to its relatively large size, it is difficult to maintain a precisely metered flow through the connecting port when the valve is opened only slightly. For example, during periods of high refrigeration demands, the suction valve should be opened only slightly (e.g., at 2.5–3.5% of maximum opening). Under those conditions, a slight inaccuracy in the amount of valve openness can produce a relatively large change in fluid flow. Achieving a precise flow is made even more difficult if the actuator is a stepping motor which can position the valve element in a only limited number of positions. In the event that the compressor is being driven by an internal combustion engine, a flow rate which is too low or even terminated, may cause the internal combustion engine to be choked.
A different problem may be encountered when a refrigeration system is shipped from a manufacturer to a customer, since there may be refrigerant in a portion of the refrigerant line situated between the expansion valve or suction valve and another valve. If the system were exposed to high enough temperatures, the refrigerant pressure could increase to such a degree that one of the valves or the piping could break.
Therefore, it is an object of the invention to provide a flow control valve capable of providing a precisely metered low flow.
Another object is to provide such a flow control valve that is actuated by a stepper motor.
Still another object is to provide such a flow control valve that can function as either an expansion valve or a suction valve in a refrigeration system.
A further object is to provide a flow control valve that can relieve high pressures generated by high temperatures encountered by the system, e.g. when being shipped or stored.